1. Field of the Invention
The present invention relates to an image forming apparatus constructed to be switchable between black monochromatic image forming and multicolor image forming using a plurality of image forming units. The present invention also relates to a drive unit for driving the image forming units, which are provided in the image forming apparatus for an image forming process therein and are easily detachable from the image forming apparatus.
2. Description of the Related Art
An apparatus having a plurality of developing units accommodating developers therein for developing electrostatic latent images is well-known as an image forming apparatus capable of forming multicolor images (a color image forming apparatus). In particular, such a well-known image forming apparatus includes a black developing unit accommodating a black developer, a yellow developing unit accommodating a yellow developer, a magenta developing unit accommodating a magenta developer, and a cyan developing unit accommodating a cyan developer.
When black monochromatic images are formed using the image forming apparatus having four kinds of developing units corresponding to the four-color developers mentioned above, it is not necessary to drive the developing units for developers other than that corresponding to the black monochromatic developer. In this case, there are known image forming apparatuses capable of preventing deterioration of the developing units and the developers other than black by stopping to drive the developing units other than the black developing unit (see Japanese Patent Application Laid-Open (kokai,) No. 2005-156779, No. 2002-6579, No. H10-307442, and No. H07-248683).
However, the image forming apparatuses disclosed in the above-mentioned Publications have been provided with switching mechanisms, such as a solenoid or an electromagnetic clutch, for switching between black monochromatic image forming and multi-color image forming (referred to as a switching mechanism below). This switching mechanism is only for switching between black monochromatic image forming and multi-color image forming, which is essentially irrelevant to driving of image forming mechanisms such as the developing units. Thus, providing such a switching mechanism unnecessarily complicates the structure of the image forming apparatus, increasing the apparatus cost.